This invention relates in general to an apparatus for machining a workpiece by electro-erosion using a wire fed through a machining zone of the workpiece.
In such an apparatus the wire electrode is fed at a predetermined longitudinal velocity to compensate for the wear of the electrode, while being transversely displaced relative to the workpiece. The displacement between the wire electrode and the workpiece is generally effected automatically by a servo system under the control of programmed instructions defining a predetermined machining path.
This invention relates more specifically to a wire electrode guide for a discharge machining apparatus.
It is known to hold an electrode in contact with guide surfaces by mechanical means as described in German Offenlegungsschrift No. 2,207,942 and British Patent No. 1,574,048.
FIG. 1 is a sectional view of such a conventional guide arrangement for a wire electrode discharge machining apparatus, wherein reference numeral 1 designates a wire electrode, 2 are individual guides disposed above and below a workpiece 3, and 4 are a pair of contacts for supplying electrical machining power from a power supply (not shown) to the wire electrode.
In such an apparatus the wire electrode 1 is fed through the machining zone while being supplied with power through the pair of contacts 4, whereby the workpiece 3 is machined in a controlled manner by electro-erosion. The servo system for effecting the relative displacement between the wire electrode and the workpiece is not shown.
The pair of contacts 4 engage the wire electrode 1 at points eccentric to a center line linking the guides 2, as shown in FIG. 1. Since the eccentric contact points are both on the same side of the wire electrode, and the inner diameter of the guides is greater by about 2-5 mm than the diameter of the wire electrode, a gap D is formed between the wire electrode and each guide as shown in FIG. 2. During the machining of the workpiece the wire electrode is acted upon by external forces, such as those produced by a machining fluid or discharge phenomena, which tend to displace the electrode within the range of the gap D between the electrode and the guides. However, since the eccentric force exerted by the contacts 4 is greater than these external forces the electrode movement is constrained in the X direction in FIG. 2. Significant displacements occur in the Y direction, however, which reduces the precision and accuracy of the machining operation. Also, since the inner diameter of the guides 2 is about 2-5 mm greater than the diameter of the wire electrode 1, it becomes necessary to replace the guides whenever the wire electrode diameter is changed.